Assessing outcomes in stratospheric aerosol injection scenarios shortly after deployment

Stratospheric aerosol injection (SAI) is a proposed form of climate intervention that would release reflective particles into the stratosphere, thereby reducing solar insolation and cooling the planet. The climate response to SAI is not well understood, particularly on short-term time horizons frequently used by decision-makers and planning practitioners to assess climate information. We demonstrate two framings to explore the climate response in the decade after SAI deployment in modeling experiments with parallel SAI and no-SAI simulations. The first framing, which we call a snapshot around deployment, displays change over time within the SAI scenarios and applies to the question "What happens before and after SAI is deployed in the model?" The second framing, the intervention impact, displays the difference between the SAI and no-SAI simulations, corresponding to the question "What is the impact of a given intervention relative to climate change with no intervention?" We apply these framings to annual mean 2 m temperature, precipitation, and a precipitation extreme during the 10 yr after deployment in two large ensembles of Earth system model simulations that comprehensively represent both the SAI injection process and climate response, and connect these results to implications for other climate variables. We show that SAI deployment robustly reduces changes in many high-impact climate variables even on these short timescales where the forced response is relatively small, but that details of the climate response depend on the model version, greenhouse gas emissions scenario, and other aspects of the experimental design.